Display with localized brightness adjustment capabilities

ABSTRACT

An electronic device may have a display with an array of pixels. The device may have an array of components such as an array of light sensors for capturing fingerprints of a user through an array of corresponding transparent windows in the display. A capacitive touch sensor, proximity sensor, force sensor, or other sensor may be used by control circuitry in the device to monitor for the presence of a user&#39;s finger over the array of light sensors. In response, the control circuitry can direct the display to illuminate a subset of the pixels, thereby illuminating the user&#39;s finger and causing reflected light from the finger to illuminate the array of light sensors for a fingerprint capture operation. The display may have display driver circuitry that facilitates the momentary illumination of the subset of pixels with uniform flash data while image data is displayed in other portions of the display.

This application is a continuation of patent application Ser. No.15/257,448, filed Sep. 6, 2016, which claims the benefit of provisionalpatent application No. 62/267,537, filed Dec. 15, 2015, both of whichare incorporated by reference herein in their entireties.

BACKGROUND

This relates generally to electronic devices, and, more particularly, toelectronic devices with displays.

Electronic devices often include displays. Displays such as organiclight-emitting diode displays have pixels with light-emitting diodes.During normal operation, the pixels are illuminated to display imagesfor a user.

In some situations, it may be desirable to provide non-imageillumination with the pixels. If care is not taken, this illuminationwill not have desired attributes.

It would therefore be desirable to be able to provide improvedelectronic devices and display arrangements for accommodating the use ofpixels to provide non-image illumination.

SUMMARY

An electronic device may have a display. The display may have an arrayof pixels such as an array of pixels with organic light-emitting diodesor other light-emitting diodes. The device may have an array ofelectrical components mounted under the display. The electricalcomponents may be an array of light sensors for capturing fingerprintsfrom a user or for gathering information on other external objects. Thelight sensors in the array may gather light readings through an array ofcorresponding transparent windows in the display.

A capacitive touch sensor, proximity sensor, light detector, straingauge sensor or other force sensor, or other sensor may be used bycontrol circuitry in the device to monitor for the presence of a user'sfinger or other object over the array of light sensors. In response todetecting the user's finger, the control circuitry can direct thedisplay to illuminate a portion of the display or all of the displaywith uniform light. For example, in a configuration in which a lightsensor array occupies a portion of a display, a subset of the pixelsthat overlaps the light sensor may be illuminated.

The illuminated subset of pixels can produce a flash of illumination ormay otherwise be adjusted in brightness independently from pixels in therest of the display. The flash may be relatively brief. For example, thelength of the flash may be equal to one frame time (e.g., 1/60 s in adisplay in which the rate at which image frames are displayed is 60 Hz).The flash may illuminate a user's finger that is adjacent to the subsetof pixels and the light sensor array. Reflected light from the user'sfinger may illuminate the array of light sensors for a fingerprintcapture operation. Illuminating the light sensors with a flash of lightfrom subset of the pixels overlapping the light sensor array (i.e., aflash region) may help ensure that fingerprint capture operations areperformed satisfactorily.

The display may have display driver circuitry that facilitates themomentary illumination of the subset of pixels with uniform flash datawhile image data or other suitable data is displayed in other portionsof the display. The display driver circuitry may have multiplexercircuitry that selectively routes either image data or flash data to aset of pixels in a fixed flash region on the display or may havemultiplexer circuitry that can be dynamically configured to place theflash region at a desired location on the display.

Further features will be more apparent from the accompanying drawingsand the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illustrative electronic devicehaving a display in accordance with an embodiment.

FIG. 2 is a top view of an illustrative display in an electronic devicein accordance with an embodiment.

FIG. 3 is a cross-sectional side view of a display with an array ofelectrical components in accordance with an embodiment.

FIG. 4 is a top view of an illustrative display with a region that isbeing used to provide flash illumination in accordance with anembodiment.

FIGS. 5 and 6 are diagrams of illustrative display driver circuitry inaccordance with an embodiment.

FIG. 7 is a timing diagram showing how image data may be loaded into adisplay in accordance with an embodiment.

FIG. 8 is a timing diagram showing how flash data may be loaded into adisplay so that a region of the display produces flash illumination inaccordance with an embodiment.

FIG. 9 is a flow chart of illustrative operations involved in loadingflash data into a display so that a region of the display produces flashillumination in accordance with an embodiment.

FIG. 10 is a diagram of illustrative display driver circuitry that maybe configured to place a flash region in a desired location on a displayin accordance with an embodiment.

FIG. 11 is a diagram of illustrative display driver circuitry of thetype that may be used to adjust display brightness in a local region ofa display independently from the rest of the display in accordance withan embodiment.

FIG. 12 is a graph in analog pixel voltage has been plotted as afunction of digital data value for a local display region and otherportions of a display with driver circuitry of the type shown in FIG. 11in accordance with an embodiment.

DETAILED DESCRIPTION

An illustrative electronic device of the type that may be provided witha display is shown in FIG. 1. As shown in FIG. 1, electronic device 10may have control circuitry 16. Control circuitry 16 may include storageand processing circuitry for supporting the operation of device 10. Thestorage and processing circuitry may include storage such as hard diskdrive storage, nonvolatile memory (e.g., flash memory or otherelectrically-programmable-read-only memory configured to form a solidstate drive), volatile memory (e.g., static or dynamicrandom-access-memory), etc. Processing circuitry in control circuitry 16may be used to control the operation of device 10. The processingcircuitry may be based on one or more microprocessors, microcontrollers,digital signal processors, baseband processors, power management units,audio chips, application specific integrated circuits, etc.

Input-output circuitry in device 10 such as input-output devices 12 maybe used to allow data to be supplied to device 10 and to allow data tobe provided from device 10 to external devices. Input-output devices 12may include buttons, joysticks, scrolling wheels, touch pads, key pads,keyboards, microphones, speakers, tone generators, vibrators, cameras,sensors (e.g., light-based proximity sensors such as infrared proximitysensors, capacitive touch sensors, force sensors such as capacitiveforce sensors and strain gauge force sensors, light detectors, etc.),light-emitting diodes and other status indicators, data ports, and otherelectrical components. A user can control the operation of device 10 bysupplying commands through input-output devices 12 and may receivestatus information and other output from device 10 using the outputresources of input-output devices 12.

Input-output devices 12 may include one or more displays such as display14. Display 14 may be a touch screen display that includes a touchsensor for gathering touch input from a user or display 14 may beinsensitive to touch. A touch sensor for display 14 may be based on anarray of capacitive touch sensor electrodes, acoustic touch sensorstructures, resistive touch components, force-based touch sensorstructures, a light-based touch sensor, or other suitable touch sensorarrangements.

Control circuitry 16 may be used to run software on device 10 such asoperating system code and applications. During operation of device 10,the software running on control circuitry 16 may display images ondisplay 14 using an array of pixels in display 14.

When it is desired to produce illumination with the pixels of display14, the software running on control circuitry 16 may use display 14 toilluminate a region of the pixels on display 14. The region may, forexample, be a rectangular portion of display 14 or a region with anothershape that serves as flash illumination for a photograph, flashillumination for a fingerprint capture operation, illumination fordocument scanning operations, or illumination for other operations inwhich an object external to device 10 is to be illuminated.

The illuminated region, which may sometimes be referred to as a flashregion or flash area, may be white or may have other colors. The colorof the flash area (e.g., the color temperature of a white flash area)may be adjusted to provide illumination with desired colorcharacteristics (e.g., to satisfy aesthetic requirements, to enhance thewarmth of a photograph, to ensure that a fingerprint capture operationis performed satisfactorily, etc.). The brightness of the flash area mayalso be adjusted. Uniform flash illumination is generally appropriate,but non-uniform patterns of illumination may be provided, if desired.

Device 10 may be a tablet computer, laptop computer, a desktop computer,a display, a cellular telephone, a media player, a wristwatch device orother wearable electronic equipment, or other suitable electronicdevice.

Display 14 may be an organic light-emitting diode display or may be adisplay based on other types of display technology. Configurations inwhich display 14 is an organic light-emitting diode display aresometimes described herein as an example. This is, however, merelyillustrative. Any suitable type of display may be used, if desired.

Display 14 may have a rectangular shape (i.e., display 14 may have arectangular footprint and a rectangular peripheral edge that runs aroundthe rectangular footprint) or may have other suitable shapes. Display 14may be planar or may have a curved profile.

A top view of a portion of display 14 is shown in FIG. 2. As shown inFIG. 2, display 14 may have an array of pixels 22 formed on substrate36. Substrate 36 may be formed from glass, metal, plastic, ceramic, orother substrate materials. Pixels 22 may receive data signals oversignal paths such as data lines D and may receive one or more controlsignals over control signal paths such as horizontal control lines G(sometimes referred to as gate lines, scan lines, emission controllines, etc.). There may be any suitable number of rows and columns ofpixels 22 in display 14 (e.g., tens or more, hundreds or more, orthousands or more). Each pixel 22 may have a light-emitting diode 26that emits light 24 under the control of a pixel circuit formed fromthin-film transistor circuitry such as thin-film transistors 28 andthin-film capacitors). Thin-film transistors 28 may be polysiliconthin-film transistors, semiconducting-oxide thin-film transistors suchas indium gallium zinc oxide transistors, or thin-film transistorsformed from other semiconductors. Pixels 22 may contain light-emittingdiodes of different colors (e.g., red, green, and blue diodes for red,green, and blue pixels, respectively) to provide display 14 with theability to display color images.

Display driver circuitry may be used to control the operation of pixels22. The display driver circuitry may be formed from integrated circuits,thin-film transistor circuits, or other suitable circuitry. Displaydriver circuitry 30 of FIG. 2 may contain communications circuitry forcommunicating with system control circuitry such as control circuitry 16of FIG. 1 over path 32. Path 32 may be formed from traces on a flexibleprinted circuit or other cable. During operation, the control circuitry(e.g., control circuitry 16 of FIG. 1) may supply circuitry 30 withinformation on images to be displayed on display 14.

To display the images on display pixels 22, display driver circuitry 30may supply image data to data lines D while issuing clock signals andother control signals to supporting display driver circuitry such asgate driver circuitry 34 over path 38. Gate driver circuitry 34 canassert appropriate gate signals (e.g., gate signals in successive rowsmay be asserted in sequence to load each frame of data). If desired,circuitry 30 may also supply clock signals and other control signals togate driver circuitry on an opposing edge of display 14.

Gate driver circuitry 34 (sometimes referred to as horizontal controlline control circuitry) may be implemented as part of an integratedcircuit and/or may be implemented using thin-film transistor circuitry.Horizontal control lines G in display 14 may carry gate line signals(e.g., scan line signals, emission enable control signals, and otherhorizontal control signals) for controlling the pixels of each row.There may be any suitable number of horizontal control signals per rowof pixels 22 (e.g., one or more, two or more, three or more, four ormore, etc.).

It may be desirable to incorporate electrical components into display 14and/or device 10. As shown in FIG. 3, for example, electrical components84 may be incorporated into device 10 under pixels 22. Components 84 maybe discrete components or may be formed as part of a common integratedcircuit or other shared component. Components 84 may, as an example, beformed as part of device 82 (e.g., an integrated circuit) or may bemounted on a printed circuit substrate.

Electrical components 84 may be audio components (e.g., microphones,speakers, etc.), radio-frequency components, haptic components (e.g.,piezoelectric structures, vibrators, etc.), may be capacitive touchsensor components or other touch sensor structures, may be temperaturesensors, pressure sensors, magnetic sensors, or other sensors, or may beany other suitable type of electrical component. With one suitablearrangement, which may sometimes be described herein as an example,electrical components 84 may be light-based components (e.g., componentsthat emit and/or detect visible light, infrared light, and/orultraviolet light).

Light-based components 84 may emit and/or detect light that passesthrough transparent windows 76 in display 14. Windows 76 may be formedin regions located between pixels 22 and may include transparentmaterials (e.g., clear plastic, glass, etc.) and/or holes (e.g.,air-filled openings or openings filled with transparent material thatpass partly or fully through substrate 36 and other display layers 74 ofdisplay 14 such as thin-film layers forming thin-film transistors andorganic light-emitting diodes).

There may be a window 76 between each pair of pixels 22 or, morepreferably, blocks of pixels 22 (e.g., blocks of tens, hundreds, orthousands of pixels) may be associated with windows 76 and electricalcomponents 84.

Examples of light-based components 84 that emit light includelight-emitting diodes (e.g., organic light-emitting diodes, discretecrystalline light-emitting diode dies, etc.), lasers, and lamps.Examples of light-based components that detect light include lightdetectors such as photodiodes and phototransistors. Some components may,if desired, include both light emitters and detectors. For example,components 84 may emit infrared light and may include light detectorstructures for detecting a portion of the emitted light that hasreflected from nearby objects such as object 86. Components of this typemay be used to implement a proximity sensor. In configurations in whichcomponents 84 include light sensors, an array of components 84 may forma light-based fingerprint sensor (e.g., when object 86 is the finger ofa user) or other light-based sensor (e.g., a light sensor that detectsthe presence or absence of a finger or other external object bydetermining when components 84 have been shadowed by object 86 so thatambient light at components 84 is reduced). The presence of a user'sfinger or other external object 86 over a given portion of display 14(e.g., over a region that includes an array of components 84) may, ifdesired, be detected using a touch sensor formed from capacitive touchsensor electrodes in display 14, a force sensor (e.g., a capacitiveforce sensor that measures force by detecting capacitance changes as auser presses on a portion of display 14, a strain gauge that measuresforce on display 14, or other force sensing structures), a lightdetector (e.g., a light detector that detects the user's finger bymeasuring shadowing of ambient light), an infrared proximity sensor orarray of infrared proximity sensors or other light-based sensors, etc.

If desired, light-based sensors such as these may sense fingerprintswhile object 86 is illuminated with light 24 from one or more of pixels22. This light may be produced by placing a region of display 14 (i.e.,a “flash region”) in a flash mode. When operating normally, the pixelsof the flash region may be used in displaying images for a user ondisplay 14. In the flash mode, pixels 22 may produce a block of solidwhite light or other illumination to briefly illuminate object 86.Pixels 22 may, for example, produce a flash of white light that lastsfor the duration of one frame of image data on display 14. The flashregion of display 14 may be aligned with a portion of display 14 thatincludes an array of windows 76 (as an example). Finger sensingcomponents such as a force sensor, capacitive touch sensor, proximitysensor, or other detector may also overlap this portion of display 14 todetect when a user's finger is present and flash illumination isappropriate.

An illustrative display with a flash region is shown in FIG. 4. In theillustrative configuration of FIG. 4, display 14 has an array of pixels22 that receive data over vertical data lines D0 . . . DF whilereceiving control signals over horizontal gate lines G0 . . . GF. Flashregion 100 may cover some or all of display 14 and may have arectangular shape, an oval shape, a shape with shape with curved edges,a shape with straight edges, a shape with a combination of curved andstraight edges, a shape with multiple discrete parts that are separatedfrom each other by intervening pixels that are actively displaying imagedata, or any other suitable shape. In the example of FIG. 4, flashregion 100 has a rectangular shape and is located near to the lower edgeof display 14. This is merely illustrative. Region 100 may have anysuitable shape. The portions of display 14 that are not included inflash region 100 may sometimes be referred to as forming a non-flashregion on display 14.

During normal image data loading operations, data lines D0 . . . DF maybe used to load image data into display 14. Rows of pixels may be loadedin sequence by issuing control signals over gate lines G0 . . . GF.

Data line voltages suitable for operating the pixels of region 100 inflash mode may be supplied to the pixels of region 100 using data linesDN . . . DM while issuing a sequence of control signals on gate lines GK. . . GL.

Illustrative display driver circuitry 100 (see, e.g., the display drivercircuitry of FIG. 2) for display 14 is shown in FIG. 5. As shown in FIG.5, circuitry 100 may include a brightness digital-to-analog converter(DAC) such as converter 102. Converter 102 may receive a digital userbrightness setting from input 104. The user brightness setting may, forexample, be an overall level of display brightness for display 14 that auser of device 10 has supplied to device 10 using input-output devices12 and/or that control circuitry 16 has determined based on other inputsuch as input from an ambient light sensor. Converter 102 may supply avoltage Vreg2 at output 106 corresponding to the display brightnesssetting received at input 104. The value of Vreg2 may, for example, berelatively high when the brightness setting is high and may berelatively low when the brightness setting is low.

Gamma block 108 may receive voltage Vreg2 from output 106 and maygenerate a set of voltages V255 . . . V0 at outputs 112 (e.g., using avoltage divider formed from a resistor tree and other circuitry). Thevalues of V225 . . . V0 may be used in establishing a desired mappingbetween digital image data values (e.g., 0 . . . 255 or other suitablerange of values) and analog voltage levels for use as analog image datasignals for the pixels of display 14. To display images on display 14,image buffer 118 may supply digital image data to gamma multiplexer 110via path 116. Gamma multiplexer 110 may supply a desired voltage fromone of lines 112 to gamma multiplexer 114 to use as data signal D inresponse to the digital image data signal received from image buffer 118on path 116. The gamma block circuitry and gamma multiplexer circuitryof display 14 may be used to supply signals to multiple data lines. Thedisplay driver circuitry of display 14 may, for example, include gammablock circuitry and gamma multiplexer circuitry that implement thefunctions of gamma block 108 and gamma multiplexer 110 of FIG. 5. Eachgamma multiplexer 110 may, for example, be associated with a respectiveone of the data lines in display 14 and may supply that data line withan appropriate data line signal.

Display 14 may contain subpixels of different colors. For example,display 14 may contain red pixels (subpixels), green pixels (subpixels),and blue pixels (subpixels). Data signals D may be demultiplexed ontocorresponding subpixel data lines 136 using data line demultiplexercircuitry such as data line demultiplexer 134. There may be ademultiplexer such as demultiplexer 134 associated with each column ofred, green, and blue pixels. During operation, the voltage on line 114may be placed in a state appropriate for a red subpixel while controlsignal MUXR is taken high to direct demultiplexer 134 to route thevoltage on line 114 to red subpixel data line R. Control signals MUXGand MUXB may likewise be asserted to demultiplex the signal on line 114onto data lines G and B.

The circuitry of FIG. 5 may be used for each of the data lines indisplay 14 that do not receive flash region data (i.e., data lines thatdo not overlap the flash region). In the example of FIG. 5, these datalines include data lines D0 . . . DN−1 and DM+1. . . DF of display 14 ofFIG. 4. Display driver circuitry of the type shown in FIG. 6 may be usedfor the data lines in display 14 that are configured to receive eitherimage data or flash data (i.e., lines DN . . . DM that overlap region100 in the example of FIG. 4). The display driver circuitry of FIG. 6includes a mode selection multiplexer circuitry for each data line (modeselection multiplexer 124). The mode of operation of the display drivercircuitry of FIG. 6 may be switched by control circuitry 16 between anormal image data loading mode and a flash data loading mode using modeselection signal MODE_SELECT.

Mode selection control signal MODE_SELECT may be deasserted whenever itis desired to route normal image data to subpixel data lines in thecolumns of display 14 associated with data lines DN . . . DM of FIG. 4.For example, MOD_SELECT may be deasserted when loading signals into therows of pixels associated with gate lines G0 . . . GK-1 and GL+1 . . .GF during image display operations (and during flash operations) and mayalso be deasserted when loading signals into the rows of pixelsassociated with gate lines GK . . . GL during image display operations.In this mode (sometimes referred to as a normal mode, image mode, ornon-flash mode), image data from a gamma multiplexer (see, e.g.,multiplexer 110 of FIG. 5) that is supplied to multiplexer 124 at input130 may be routed to line 132. Demuliplexer 134 may demultiplex thissignal onto subpixel data lines 136.

Mode selection control signal MODE_SELECT may be asserted whenever it isdesired to route flash data Df from line 128 to line 132 for loadinginto the pixels of flash region 100 (e.g., when loading signals intoregion 100 using data lines DN . . . DM and using gate lines GK . . . GLduring flash mode operations in the example of FIG. 4).

Flash data signals Df may be generated by flash digital-to-analogconverter 122 based on a digital flash setting signal that controlcircuitry 16 supplies to converter 122 at control input 120. Converter122 may produce different values of Df for different flash brightnesslevels. For example, converter 122 may produce a relatively largevoltage Vf for use as flash data Df when the flash setting on input 120is set to a “high” setting, may produce a relatively low voltage Vf whenthe flash setting on input 120 is set to a “low” setting, and mayproduce an intermediate voltage Vf when the flash setting on input 120is set to a “medium” setting. When high data values Df are loaded intothe pixels of flash region 100, the pixels of region 100 will producebright output. The use of medium or low data values Df will result incorresponding medium or low output light levels from region 100. The useof three different brightness settings is merely illustrative. Converter122 may support more than three different brightness levels or fewerthan three different levels. Converter 122 may also produce data valuesDf that are different for the subpixels of different colors in region100. This allows the color temperature or other color attributes of theoutput light produced by flash region 100 to be adjusted. Coloradjustments may be made independently of brightness level adjustments ordifferent colors may be associated with different brightness levels.Flash data Df is generally uniform across region 100 (i.e., all ofpixels 22 in region 100 receive the same data: the same red subpixelvalue, the same green subpixel value, and the same blue subpixel value).If desired, data Df can be varied within region 100 to create flashillumination with a non-uniform intensity pattern.

FIG. 7 is a timing diagram showing how image data D may be loaded intothe pixels of display 14. Pixels 22 may be loaded with image data usingcircuitry of the type shown in FIG. 5 and using circuitry of the typeshown in FIG. 6 while signal MODE_SELECT is deasserted.

As shown in FIG. 7, demultiplexer control signals MUXR, MUXG, and MUXBfor demultiplexer 134 may be asserted in sequence while the circuitry ofeach gamma block 108 and each gamma multiplexer 110 is being used toproduce desired values of data signal D on each data line 114. As MUXRis asserted, the current value of D is routed to a column of redsubpixels. Assertion of MUXG and MUXB likewise are used to route thecurrent value of D for each data line to columns of green and bluepixels, respectively. MODE_SELECT may be deasserted during the loadingof normal image data to ensure that the data signals that are suppliedto input 130 of multiplexer 124 of FIG. 6 are routed to data line 132.

FIG. 8 is a timing diagram showing how flash data Df may be loaded intothe pixels of region 100. During flash data loading operations,MODE_SELECT may be asserted to ensure that the flash data signals thatare supplied to input 128 of multiplexer 124 of FIG. 6 from converter122 are routed to data line 132. As shown in FIG. 8, demultiplexercontrol signals MUXR, MUXG, and MUXB for demultiplexer 134 may beasserted in sequence while gamma converter 122 is being used to producedesired values of data signal Df on each data line 114 for each of thedifferent colors of subpixels in region 100. As MUXR is asserted, thecurrent value of Df is routed to a column of red subpixels. Assertion ofMUXG and MUXB may likewise be used to respectively route the currentvalue of Df to columns of green and blue pixels in region 100. Asidefrom changing the value of Df for each subpixel color, the value of Dfis generally not changed so that all of region 100 is illuminateduniformly. Configurations in which region 100 is not illuminateduniformly may be handled by directing converter 122 to vary the value ofDf for different portions of region 100.

FIG. 9 is a flow chart of illustrative steps involved in loading imagedata and flash data into pixels 22 of display 14.

During the operations of step 140, the display driver circuitry of FIG.5 and FIG. 6 may load image data into each of the rows of display 14that do not overlap flash region 100. As an example, gate lines G0 . . .GK-1 may be asserted in sequence while image data is presented to alldata lines D0 . . . DF.

In situations in which no flash data is to be presented (e.g., insituations in which flash region 100 is being used to display an imageand is not being used to produce flash illuminations), the operations ofstep 140 may be used to load data into all rows of display 14 (e.g.,rows GK . . . GF) while image data is presented to all data lines D0 . .. DF. Once an entire frame of image data has been loaded into display 14and displayed for a user, processing may loop back to step 140, asindicated by line 142, so that another frame of image data may beprocessed.

In situations in which flash data is to be presented in flash region100, signal MODE_SELECT may be asserted (step 144). During step 144, thegate lines of display 14 that overlap flash region 100 may be assertedin sequence. At the same time, image data may be presented to the datalines that do not overlap the flash region while flash data issimultaneously presented to the data lines that do overlap the flashregion. The remainder of the pixels in display 14 (i.e., the pixels inrows below the flash region, if any) may then be loaded with image databy deasserting MODE_SELECT and processing initiated for a fresh frame(step 140).

If desired, the display driver circuitry for display 14 may beconfigured to allow the position of flash region 100 to be adjusted bycontrol circuitry 16. This approach may be used, for example, to allow afingerprint(s) to be captured at a number of different locations ondisplay 14.

Consider, as an example, the illustrative display driver circuitry ofFIG. 10. In the example of FIG. 10, the gamma multiplexers of display 14are provided with a first input that receives the output of gamma block108 and a second input that receives flash data Vf from the output ofconverter 122. A flash control signal (e.g., FLASH_MODE) may be suppliedto each gamma block 108. When FLASH_MODE is deasserted for the gammamultiplexer 110′ for a given data line 114, that data line is providedwith image data signals D from the gamma block 108 at the first input ofthat gamma multiplexer 110′. This allows normal data to be loaded ontosubpixel data lines 136. When FLASH_MODE is asserted for the gammamultiplexer 100′ for a given data line 114, that data line is providedwith flash data signals Df from the flash digital-to-analog converter122 at the second input of that gamma multiplexer 110′.

The flash mode selection input for the gamma multiplexer circuitry maybe used to adjust the position of the flash region. The inputs for eachof gamma multiplexers 100′ may all be independent or groups of two ormore of these inputs may be connected together to conserve circuitresources. In situations in which the FLASH_MODE signal in each columnis independently adjustable by control circuitry 16, control circuitry16 can select a pattern of asserted and deasserted FLASH_MODE signals toadjust the horizontal position of flash region 100 to any desiredlocation within display 14. In situations in which there are fewerindependently adjustable FLASH_MODE signals, the available horizontalpositions for region 100 will be correspondingly restricted, but fewerdifferent control lines will be required. Vertical positioning of region100 may be implemented by asserting FLASH_MODE in appropriate columnswhile a set of gate lines that overlap the desired position of region100 are being asserted.

During manufacturing, display 14 may be calibrated. For example, testimage data may be displayed on display 14 while image calibrationmeasurements are made and test flash data may be displayed in a testflash region of display 14 while flash calibration measurements aremade. Resulting calibration data for display 14 (e.g., global imagecalibration data, region-specific image calibration data, pixel-by-pixelimage calibration data, and flash region calibration data for allpixels, blocks of pixels, or each pixel in flash region 100) can then bestored in display 14 and used in producing calibrated image data withgamma block 108 and in producing calibrated flash illumination.

Control circuitry 16 may monitor sensors and other input-output devices12 to determine when to initiate flash mode operations. For example,circuitry 16 may monitor input from a capacitive touch sensor todetermine when a user's finger has been placed over flash region 100.The flash region can then be illuminated so that an array of lightdetectors 84 in this region can be used to capture a fingerprint (as anexample). If desired, other types of sensor input can be processed bycontrol circuitry 16 to determine when a user's finger or other objectis in flash region 100 for fingerprint capture. For example, components84 or other components in device 10 may include infrared emitters andsensors that form light-based proximity sensors. When a proximity sensorreading indicates that a user's finger is present, control circuitry 16can illuminate region 100 and gather sensor readings from an array oflight sensor components 84. In some situations, components 84 (e.g.,light sensors) may output signals with a given level during normalambient lighting conditions and may exhibit output signals with atemporarily reduced level when normal ambient lighting conditions arestill present but a finger or other object is shadowing components 84.Force sensors (capacitive sensors, strain gauges, etc.) may be use todetect the presence of a users finger. In general, proximity sensormeasurements, capacitive touch sensor measurements, ambient light sensorshadow detection, actuation of a force sensor (e.g., a strain gauge,etc.), actuation of a switch under region 100, or other suitablearrangements may be used in determining when to activate flash region100 and capture a fingerprint. The foregoing examples are merelyillustrative.

In operations such as fingerprint capture operations, it may bedesirable for the illumination provided by the pixels of flash region100 to be uniform. Accordingly, each of the pixels in this region may beprovided with the same flash data Df. The color of the light produced inregion 100 can be adjusted by adjusting the relative magnitude of theoutput produced by the red, green, and blue subpixels (or subpixels ofother suitable colors) within this uniform data for region 100. Ifdesired, different portions of region 100 can be provided withcorrespondingly different values of data Df (e.g., to produce patternedflash illumination, graded flash illumination, or flash region outputwith other non-uniform characteristics). Moreover, the non-flash regionof display 14 may be used to display output with a particular brightness(normal, higher than normal, or lower than normal), a particular color(blue, green, red, or other colors), may be used to display a pattern ofnon-image data, may be used to display modified image data, or may beused to display other desired output during the use of flash region 100to produce flash output. The use of the non-flash regions of display 14to display normal image data while flash region 100 supplies uniformflash output is merely illustrative.

If desired, display 14 may be provided with a first region (e.g., region100 of FIG. 4 or any other suitable portion of display 14) that has abrightness that is independently adjustable from the brightness of asecond region of display 14 (e.g., the rest of display 14 of FIG. 4outside of region 100). The brightness (maximum pixel luminance) in thefirst and second regions may be independently adjusted by using separatebrightness control signals for the first and second regions. Using thistype of arrangement, a local area of display 14 (e.g., region 100) maybe provided with a boosted brightness for illumination purposes (e.g.,to serve as a flash illumination for an array of light sensors, etc.) ormay be provided with a locally dimmed or brightened appearance toenhance a user's interaction with content in the locally dimmed orbrightened local area.

FIG. 11 is a diagram of illustrative display driver circuitry of thetype that may be used to adjust display brightness in a local region ofa display independently from the rest of the display. The display drivercircuitry of FIG. 11 may handle an expanded gamma. For example, insteadof converting digital image data into 256 gray voltage levels, thedisplay driver circuitry of FIG. 11 may convert digital image data andbrightness control data into 1024 voltage levels.

As shown in FIG. 11, image data mapping circuitry 150 may receive 8-bitimage data and may produce corresponding 10-bit gamma block digitalinput data for gamma multiplexer circuitry 110 on path 116′. Circuitry150 therefore maps 8-bit input image data to 10-bits of output data onpath 116′ at the digital input to gamma multiplexer circuitry 110 tocover up to 1024 voltages levels. The maximum luminance associated withthese 1024 values may exceed the maximum luminance available in acomparable 256 level system (as an example), so that display 14 canexhibit locally enhanced brightness. The ability of display 14 toexhibit enhanced display brightness can be provided to all of the pixelsin display 14 (i.e., all of display 14 may have pixels 22 that areprovided with up to 1024 voltage levels) or only portions of display 14may have the ability of display 14 to exhibit enhanced displaybrightness (i.e., only pixels 22 in region 100 may receive up to 1024voltage levels over corresponding data lines 114).

Mapping circuitry 150 may include 8-bit to 10-bit mapping circuits 156and 158. Circuit 158 may receive local brightness control signals onbrightness control input 154 for a region such as region 100 and circuit156 may receive brightness control signals on brightness control input152 for the rest of display 14. Image data for local region 100 ofdisplay 14 may be provided to mapping circuit 158 from image buffer 118at input 116A. Image data for the rest of display 14 may be provided tomapping circuit 156 from image buffer 118 at input 116B. The image dataat inputs 116A and 116B may be 8-bit data or may have any other suitablebit size. The corresponding output data on path 116′ may be 10-bit dataor may have any other suitable size larger than the input data.

Mapping circuitry 150 may produce an output that is based on the imagedata and brightness control data presented to the inputs of mappingcircuitry 150. Mapping circuit 158 may, for example, produce an outputthat is equal to the product of the grey level (image data) presented atinput 116A and the brightness control signal for region 100 that ispresented at input 154, whereas mapping circuit 156 may produce anoutput that is equal to the product of the grey level (image data)presented at input 116B and the brightness control signal for the regionof display 14 other than region 100 that is presented at input 152.

There may be two separate sets of gamma mappings for region 100 and therest of display 14 (i.e., two corresponding sets of curves relatinginput digital data values to the analog voltage levels produced bycircuitry 110 for pixels 22). Consider, as an example, the gamma curvesof FIG. 12, which include a first set of curves (curves 160) and asecond set of curves (curves 164). Each of the curves in each set ofcurves corresponds to a different brightness setting. In the example ofFIG. 12, the maximum pixel luminance in region 100 corresponds to analogpixel voltage V[1023] and is larger than the maximum pixel luminance inthe rest of display 14, which corresponds to analog pixel voltage VM.This is merely illustrative. The maximum pixel luminance for region 100and the rest of display 14 may be the same or region 100 may have amaximum pixel luminance that is lower than the rest of display 14.

In the illustrative configuration of FIG. 12, curves 160, whichcorrespond to region 100, show how the pixels in region 100 may have amaximum luminance that lies within range 162 (i.e. a value from V[0] toV[1023]), depending on the current brightness setting at input 154.Curves 162, which correspond to the rest of display 14, show how thepixels in the rest of display 14 may have a maximum luminance that lieswithin range 166 (i.e., a value from V[0] to VM), depending on thecurrent brightness setting at input 152.

The brightness of the content in region 100 can be adjusted usingbrightness setting 154 independently of the brightness of the content inthe rest of display 14, which is adjusted using brightness setting 152.Region 100 can have a momentarily enhanced brightness (e.g., to producea flash of illumination in configurations in which region 100 containsan array of light sensors 84) or can be provided with enhancedbrightness for longer periods of time. While the brightness setting forregion 100 is being momentarily enhanced, the digital image datacorresponding to region 100 can be provided with a single value (e.g.,to produce a block of solid white illumination) or may correspond to apattern or part of an image. If desired, the independence of thebrightness adjustments for region 100 and the rest of display 14 may beused to reduce the brightness of the pixels in region 100 relative tothe pixels in the rest of display 14. The use of separate brightnessadjustments for region 100 and the rest of display 14 to produce amomentarily enlarged brightness in region 100 is merely illustrative.

The foregoing is merely illustrative and various modifications can bemade by those skilled in the art without departing from the scope andspirit of the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. An electronic device, comprising: an array ofdisplay pixels configured to emit light; and a sensor at least partiallycovered by the array of display pixels, wherein the sensor is configuredto sense a foreign object illuminated by the light emitted from thearray of display pixels, and wherein the sensor is further configured tomeasure the illumination of the foreign object by detecting lightreflecting from the foreign object and traversing through the array ofdisplay pixels.
 2. The electronic device of claim 1, wherein the sensoris further configured to capture a fingerprint illuminated by the lightemitted from the array of display pixels.
 3. The electronic device ofclaim 1, wherein the array of display pixels is formed in a plurality ofdisplay layers, and wherein the light reflecting from the foreign objecttraverses through transparent windows in the plurality of displaylayers.
 4. The electronic device of claim 1, wherein the sensorcomprises an optical sensor.
 5. The electronic device of claim 1,wherein the array of display pixels is configured to display flash datato illuminate the foreign object.
 6. The electronic device of claim 1,wherein the array of display pixels is configured to display uniformdata to illuminate the foreign object.
 7. The electronic device of claim1, wherein the array of display pixels is configured to display uniformflash data to illuminate the foreign object.
 8. The electronic device ofclaim 1, further comprising: control circuitry configured to direct afirst region of the array of display pixels to display image data and todirect a second region of the array of display pixels to display flashdata to illuminate the foreign object, wherein the control circuitry isfurther configured to adjust the location of the second region.
 9. Anelectronic device, comprising: an array of light-emitting elements; andan optical sensor formed directly under the array of light-emittingelements, wherein the optical sensor is configured to capture afingerprint by illuminating the fingerprint using the array oflight-emitting elements and measuring the corresponding illumination viaopenings in the array of light-emitting elements.
 10. The electronicdevice of claim 9, wherein the array of light-emitting elementscomprises an array of display pixels.
 11. The electronic device of claim10, wherein the array of display pixels comprise an array of organiclight-emitting diode (OLED) pixels.
 12. The electronic device of claim9, wherein the array of light-emitting elements is configured to displayimage data.
 13. The electronic device of claim 12, wherein the array oflight-emitting elements is further configured to display flash data thatis different than the image data.
 14. The electronic device of claim 13,wherein only a portion of the array of light-emitting elements is usedto display the flash data.
 15. The electronic device of claim 13,further comprising: control circuitry configured to direct a firstregion of the array of light-emitting elements to display the image dataand to direct a second region of the array of light-emitting elements todisplay the flash data, wherein the control circuitry is furtherconfigured to adjust the placement of the second region.
 16. Anelectronic device, comprising: an array of display pixels having a firstregion and a second region; control circuitry configured to direct thedisplay pixels in the first region to display image data while using thedisplay pixels in the second region to capture a fingerprint, whereinthe control is further configured to adjust the position of the secondregion; and multiplexing circuitry configured to drive the array ofdisplay pixels, wherein the control circuitry adjusts the position ofthe second region by controlling a mode selection input that is providedto the multiplexing circuitry.
 17. The electronic device of claim 16,wherein the control circuitry is further configured to select a patternof asserted and deasserted flash mode signals to adjust the horizontalposition of the second region.
 18. The electronic device of claim 16,wherein the control circuitry is further configured to select a patternof asserted and deasserted flash mode signals to adjust the verticalposition of the second region.
 19. The electronic device of claim 16,wherein the control circuitry is further configured to direct thedisplay pixels in the second region to output uniform flash data that isdifferent than the image data.